This is a gift that keeps on giving.
After initial success with putting a spare into rotation, i have decided to do it again, and once again i was able to single out the worst tire. Doing so resulted in the best ride i have had so far:
55 - smooth
60 - smooth
65 - slight shake
70 and above - stabilizes to tolerable levels.
By "tolerable" i mean not perfect, it is not bad, but if i had to be a picky princess then there you have it. Actually it is on part with driving on a highway in north east region - road seems smooth, but not smooth enough.
Got tires into another shop for another rebalance and reading:
LF: 15 RF: 5
LR: 16 RR: 7
Spare (the worst) : 19
So they are withing acceptable 20 lb range, but persisting issue is persisting issue. Personally i don't care what this numbers mean, what matters to me if there is a correlation between a high number and bad riding characteristic of a tire, which in this case seems to be the case. The spare tire is a trouble maker and balancing machine singles it out as well.
This time a "precision" method was used to balance tires. I went from static, to dynamic and now precision.
After rebalance, things have stayed the same, it is as smooth as it ever was up to 65, shaking at 65 and gets better at 70.
When i move spare (the worst) to the front, ride gets worse.
When i move spare to the rear, ride gets better but it is difficult to say if it is better than without it. At this point i need to purchase a vibration analyzer that can keep track of this mess.
Balancing beads - as if did not have enough shit on my plate as is.
How much beads does a tire need? One maker calls for 4oz, another say 6oz, and of course another one would say 8oz.
I went with 8oz because <enter your reason>
One tire at a time i started replacing wheel weights with beads. I did it this way to see if i can single out another bad tire.
*NOTE 1* Beads will not work with wheel weights, they need unbalanced tire to work. I tried and i thought my wheel was gonna fly off.
*NOTE 2* Tires were rotated, front and rear swapped. Additionally bad spare tire is now on RR.
LF tire went well, just as good or better. This tire also needed the most weights (12 oz: 6oz and 6oz diametrically opposite of it), and this i think is key factor to why this experiment went down the hill from here.
RF tire did not do so well, shakes starting at 50 and persisting to 70 and above. This tire was asking for 2.75oz
RR tire with beads has also worsen the shake, this one called for 3.25oz and shake felt bias to passenger side.
RL tire evened out the shake.
At this point it does not matter what is going on with 5th tire.
Based on what i have experienced, now i have a theory that amount of unbalance has to be proportional to amount of beads put into a tire. In another words, i think there is a threshold after which beads will do more harm.